Self-correcting, high fidelity, sound reproducing apparatus



Oct. 9, 1962 w. M. TURNER' 3,057,961

SELF-CORRECTING, HIGH FIDELITY, SOUND REPRODUCING APPARATUS Filed Jan.8, 1959 2 Sheets-Sheet l 60 54F f mmuz/vcr MHDULATED mm'M/MTfiWL/HER wars/slv/u man/25p INVENTOR. WHEELER M: TURNER Oct. 9, 1962 w. M. TURNER3,057,961

SELF-CORRECTING, HIGH FIDELITY, SOUND REPRODUCING APPARATUS Filed Jan.8, 1959 2 Sheets-Sheet 2 FEEDBACK ANPL IF IE1? aq vsaucfk L a /s f 20FEEDBACK TRANSDUCER INVENTOR. /ac WHEELER M.TURNER United States Patent3,057,961 SELF-CURREQTENG, HEGH FIDELITY, SOUND REPRGDUQING AEPARATUSWheeler M. Turner, Santa Barbara, Calif, assignor to Security FirstNational flank, Los Angeles County,

Calif a national banking association Filed .ian. S, 1959, Ser. No.735,733 6 Claims. (Cl. 1791) The present invention consists ofself-correcting, high fidelity, sound reproducing apparatus of a typecomprising electroacoustic sound-producing transducer means including amechanically vibratable output element effectively coupled to ambientatmosphere, including electrical input circuit means, and includingelectro-mechanical translating motor means effectively electricallyenergizably coupled to the electrical input circuit means andeffectively drivingly coupled to the mechanically vibratable outputelement for vibrating same in a manner corresponding to a variableelectric input signal fed into the electrical input circuit means, andfurther including capacitive mechano-electrical feedback transducermeans including a vibratable input element and a second element incapacitive relationship to each other, with the vibratable input elementof the feed back transducer means being eifectively coincident with thevibratable output element of the sound-producing transducer means, andwith said two elements of said feedback transducer means beingeifectively electrically coupled, in negative feedback relationship,with respect to the electrical input circuit means, which in onepreferred form may include amplifier means.

It should be noted that in one preferred form of the present invention,the vibratable input element of the capacitive negative feedbacktransducer means. comprises an electrically conductive thin-sheet membercoextensive with a substantial portion of the surface area (usuallysubstantially the entire surface area) of the vibratable output elementof the sound-producing transducer means whereby to eifectively integrateand sum vibratory variations in different portions of the vibratableoutput element.

It should be noted that in one preferred specific form of the invention,the electro-mechanical translating motor means of the electroacousticsound-producing transducer means may take the form of electromagneticmotor means consisting of a voice coil and a permanent magnet providinga magnetic field encompassing said voice coil, with said voice coilbeing effectively electrically energizably coupled to the electricalinput circuit means, which in one preferred form includes amplifiermeans.

It should also be noted that, in one preferred specific form of theinvention, the mechanically vibratable output element of theelectroacoustic sound-producing transducer means may include a conicalmember having its interior conical surface coupled to ambientatmosphere.

It should also be noted that in one preferred form of the invention, thevibratable input element of the capacitive negative feedback transducermeans may comprise a conical electrically conductive thin-sheet membercoextensive with substantially the entire conical surface area of atleast one side of (preferably the front side of) the conical vibratableoutput element of the soundproducing transducer means, while the secondelement of the feedback transducer means may comprise an electricallyconductive frame means mounting the conical mechanically vibratableoutput element of the sound-producing transducer means.

In other words, one preferred form of the invention may comprise aconventional type loudspeaker wherein the loudspeaker cone carries oneither the front or rear ice surface thereof an electrically conductivecoating, such as conductive silver paint or the like, adapted to bemechanically vibrated by the loudspeaker cone in capacitive relationshipwith respect to the electrically conductive metallic frame mounting theentire loudspeaker, and with said electrically conductive coating andsaid electrically conductive frame together comprising theabovementioned capacitive negative feedback transducer means and beingeffectively connected, in a negative feedback sense, to amplifier meansin the electrical input circuit means eifectively driving the voice coilof the conventional loudspeaker.

The specific negative feedback loudspeaker arrangement just describedhas several distinct and very important advantages over prior artloudspeaker systems. For example, any distortion or production ofspurious sound occurring as a result of imperfect action of theloudspeaker conein other words, action of the loudspeaker cone in amanner other than as the perfect piston which it is supposed tosimulate-such as cone breakup, standing waves, and the like, will becorrected and compensated for by the improved apparatus of the presentinvention because the capacitive mechano-electrical negative feedbacktransducer, consisting of the electrically conductive coating carried bythe loudspeaker cone and the closely adjacent metallic loudspeaker framein association with the electrical circuit components connected thereto,causes an error signal to be produced by portions of the cone havingspurious vibrations not corresponding to the correct signal fed to thevoice coil and occurring as a result of cone break-up, standing waves,and the like, which error signal is fed to the driving amplifier in anegative feedback sense in a manner which will cause mechanical movementof the voice coil and cone in exact opposition to the spuriousvibrations of the cone, to a degree such as to effectively completelycancel them out, leaving only the proper or correct vibratory mechanicaloutput of the cone corresponding to the correct electrical signal fed tothe voice coil. In other Words, the apparatus of the present inventionvirtually completely corrects and compensates for the distortionnormally present in virtually all loudspeaker systems and occurring as aresult of cone break-up, standing waves, and the like.

It should be noted that the integrating and summing feature of thecapacitive mechano-electrical negative feedback transducer means, whicheffectively integrates and sums the vibrations of virtually the completesurface area of the loudspeaker cone, is an extremely important aspectof the present invention, since this is the feature which results invirtually complete correction of and compensation for all spuriousoutput from. the loudspeaker cone, which normally occurs as a result ofcone break-up, standing waves, and the like. i

It should further be noted that the arrangement just described also hasthe effect of extending the frequency response characteristics. of thesystem as compared to conventional loudspeaker sound reproducingsystems. This is particularly true at the low frequency end of the soundspectrum, since the very substantial attenuation which normally occursat the low frequency end of the sound spectrum is substantially modifiedby the negative feed back feature of the above-described arrangement ofthe present invention to an extent such as to provide a considerableextension of and flattening of the low frequency response curve orcharacteristic of such a sound reproducing system.

It should also be noted that the sound reproducing apparatus of thepresent invention additionally provides a substantial degree ofself-correction and compensation for acoustic variations affecting thereproduction of sound and occurring as a result of changed environmentalconditionsfor example, enclosure resonance, room resonance, or otherconditions of the enclosure or room in which the sound reproducingapparatus of the present invention is placed. These conditionsfrequently may cause undesirable peaks and/or valleys to occur atcertain locations in the sound frequency spectrum of the radiated audioenergy. However, the self-correcting summing and integrating negativefeedback arrangement of the present invention provides a verysubstantial degree of correction and compensation for such peaks andvalleys arising from special acoustic conditions of the region in whichthe sound reproducing apparatus is to operate, whereby to greatlyflatten the frequency response curve by substantially eliminating suchpeaks and/or valleys therein.

With the above points in mind, it is an object of the present inventionto provide an improved self-correcting, high fidelity, sound reproducingapparatus wherein a mechanically vibratable output element coupled toambient atmosphere carries an electrically conductive thinsheet memberor coating comprising one plate of a capacitive mechanoelectricalnegative feedback transducer means having what amounts to a secondusually fixed plate closely spaced and in capacitive relationship withrespect thereto, and wherein said capactive mechano-electrical negativefeedback transducer means is connected, in a negative feedback sense, toan electrical input circuit means driving the mechanically vibratableoutput element by electro-mechanical translating motor means (usually ofthe electromagnetic type).

It is a further object of the present invention to provideself-correcting, high fidelity, sound reproducing apparatus of thecharacter set forth in the preceding object, wherein said second plateof the capacitive mechano-electrical negative feedback transducer meanscomprises the electrically conductive frame means of a loudspeaker,wherein the mechanically vibratable output element consists of theconventional loudspeaker cone, and wherein the effectively vibratableplate of the capacitive mechano-electrical negative feedback transducermeans comprises a thin metallic coating, such as silver paint, or thelike, coextensive with substantially the entire surface area of (usuallyof one side of) the loudspeaker cone to provide the effectiveintegration and summing of all spurious error signals produced by thecone, for self-correcting application in a negative feedback sense tothe speaker cone-driving amplifier. It is a further object of thepresent invention to provide a self-correcting, high fidelity, soundreproducing apparatus of the character set forth in any of the precedingobjects, wherein the electrical input circuit means includes amplifiermeans having a control electrode, and wherein said control electrode iseffectively coupled, in a negative feedback sense, to said capacitivemechano-electrical negative feedback transducer means.

It is a further object of the present invention to provideself-correcting high fidelity sound reproducing apparatus of thecharacter set forth in any of the preceding objects including polarizingmeans for applying a potential of the proper polarity to the capacitivemechano-electrical negative feedback transducer means and also includingcapacitive-discharge-restricting circuit means connected thereto toprovide a conventional type electrostatic transducer.

It is a further object to provide a self-correcting high fidelity soundreproducing apparatus of the character set forth in the precedingobject, wherein the polarizing means and thecapacitive-discharge-restricting circuit means are connected between thecapacitive mechanoelectrical negative feedback transducer means and anamplifier means, and comprise a cathode follower electron tube andassociated circuitry.

It is a further object to provide a modified form of the inventionwherein the capacitive mechano-electrical negative feedback transducermeans is not of the elecill) trostatic type but is of a type wherein theresonant frequency of a tuned circuit is varied by the capacitivevariations, is amplified, and is subsequently discriminated to providecorresponding amplitude variations which are then fed into the voicecoil driving amplifier in a negative feedback sense.

It is a further object of the present invention to provideself-correcting, high fidelity, sound reproducing apparatus of thecharacter set forth in any of the preceding objects, which is adapted tovery effectively compensate and correct for spurious audio outputproduced by speaker cone break-up, standing waves, and other types ofdistortion not corresponding to the correct electrical signal fed into aloudspeaker voice coil; the self-correction and compensation being suchas to oppose all such spurious audio output in a manner effectivelycancelling and nulling out same.

It is a further object of the present invention to provide aself-correcting, high fidelity, sound reproducing apparatus of thecharacter set forth in any of the preceding objects, adapted to correctfor distorted audio output occurring as a result of peculiar surroundingenvironmental conditions, by decreasing the audio output in thoseregions of the frequency response curve where said peculiarenvironmental conditions tend to increase the audio output, and byincreasing the audio output in those regions of the frequency responsecurve where said peculiar environmental conditions tend to decrease theaudio output.

It is a further object of the present invention to provideself-correcting, high fidelity, sound reproducing apparatus of thecharacter set forth in any of the preceding objects, which by reason ofthe integrating and negative feedback feature of the invention, providesextended frequency response. This is particularly evident at the lowfrequency end of the sound spectrum where the audio output is greatlyattenuated in conventional sound reproducing systems.

It is a further object of the present invention to provide aself-correcting high fidelity sound reproducing apparatus including aplurality of loudspeakers each having a capacitive mechano-electricalnegative feedback transducer means connected to a single drivingamplifier means or to a single cathode follower circuit connected to adriving amplifier means, whereby the combination system will provide avery efficient and self-correcting sound reproducing system capable ofradiating a very large audio output, self-corrected as hereinbeforedescribed.

It is a further object of the present invention to provide apparatus formeasuring the characteristics of loudspeaker systems and the like andincluding the mechanoelectrical transducer means, which produces avoltage which may be directly measured and which is indicative of thetotal sound generated by the loudspeaker cone regardless of directivitypatterns.

Further objects will be apparent to persons skilled in the art after acareful study hereof.

For the purpose of clarifying the nature of my invention, severalexemplary embodiments are illustrated in the hereinbelow-describedfigures of the accompanying drawings and are described in detailhereinafter.

FIG. 1 is a schematic diagrammatic view illustrating one embodiment ofthe present invention.

FIG. 2 is a schematic diagrammatic view illustrating a second embodimentof the present invention including an additional stage of amplificationbetween the feedback transducer and the voice-coil-driving amplifier.

FIG. 3 is a schematic diagrammatic view generally similar to FIG. 2 butslightly more specific in nature and showing considerably more detail ofone specific form of loudspeaker and capacitive feedback transducer.

FIG. 4 is a schematic diagrammatic view very similar to FIG. 3 butincludes an additional stage of amplification between the capacitivefeedback transducer and the voicecoil-driving amplifier.

FIG. is a larger-scale fragmentary view, partly in vertical section,showing a small portion of the capacitive feedback transducer and theconnection of leads to the metallic loudspeaker frame and the conductivecoating carried by the speaker cone.

FIG. 6 is another and more detailed electrical schematic view showingone specific embodiment of the present invention corresponding to theversion shown in FIG. 4. This view shows the loudspeaker in diagrammaticform but shows the electrical components of the capacitive feedbacktransducer and the feedback amplifier in detail.

FIG. 7 is a view very similar to FIG. 5 but shows a slight modificationof the invention wherein the conductive coating carried by the cone ison the rear surface thereof rather than on the front surface thereof.

FIG. 8 is a schematic view generally similar to FIG. 2 but illustrates aslightly modified form having a capacitive feedback transducer of thefrequency modulation type including an intermediate amplification stageand a frequency discrimination stage coupled to the voice-coildrivingamplifier.

The self-correcting, high fidelity, sound reproducing apparatus of thepresent invention, broadly speaking, includes eleetroacousticsound-producing transducer means having a mechanically vibratable outputelement effectively coupled to ambient atmosphere, having electricalinput circuit means and electromechanical translating motor meanseffectively electrically energizably coupled to the electrical inputcircuit means and effectively drivingly coupled to the mechanicallyvibratable output element for vibrating same in a manner correspondingto a variable electric input signal fed into the electrical inputcircuit means. it also includes capacitive mechano-electrical negativefeedback transducer means having a vibratable input element and a secondelement in capacitive relationship to each other, with the vibratableinput element of the feedback transducer means being effectivelycoincident with the vibratable output element of the soundproducingtransducer means, and with the two elements of the feedback transducermeans being effectively electrically coupled, in negative feedbackrelationship, with respect to the electrical input circuit means.

In the specific example illustrated in FIG. 1 in schematic diagrammaticform, the electroacoustic soundproducing transducer means is indicatedgenerally at It) and is shown as comprising a conventional typeloudspeaker, although it is not so limited. The mechanically vibratableelement of the sound-producing transducer means indicated generally at10 is designated in schematic diagrammatic form by the arrow 11 in FIG.1, and in the loudspeaker form of the sound-producing transducer means10 shown in FIG. 1, this would comprise a conventional loudspeaker cone,such as is shown in greater detail at 26 in FIG. 3, for example. In thespecific example of the invention shown in diagrammatic form in FIG. 1,the electrical input circuit means referred to above is indicatedgenerally at 12 and includes the input leads 13 and 14, the drivingamplifier 15 connected thereto, and the leads 16 and 17 connected fromthe driving amplifier to the above-mentioned electro-mechanicaltranslating motor means, which is indicated diagrammatically at 18 inFIG. 1 and, in the loudspeaker form of sound-producing transducer means.shown in FIG. 1, comprises electromagnetic motor means of a type such asis shown in greater detail in certain of the other figures, and which isdrivingly coupled to the mechanically vibratable element or loudspeakercone diagrammatically indicated by the arrow 11 in FIG. 10 and of a typesuch as is shown at 26 in FIG. 3, for example.

In the specific example illustrated in FIG. 1, the capacitivemechano-electrical negative feedback transducer means is indicated indiagrammatic form at 20 and is shown as being directly operated orvibrated by the mechanically vibratable output element or loudspeakercone of the loudspeaker 10, as indicated by the arrow 11 extending fromthe loudspeaker 10 to the feedback transducer 20. It should beunderstood that the feedback transducer 20 is merely shown indiagrammatic form and, in one preferred form which comprises acapacitive transducer, the variable capacitor thereof is actuallycarried by and effectively comprises a part of the loudspeaker 10, in amanner which will be shown in greater detail in certain of the otherfigures and described in greater detail hereinafter. In the specificexample illustrated in FIG. 1, the feedback transducer indicatedgenerally at 20 is connected by leads 21 and 22 to the driving amplifier15; this connection being in a negative feedback sense such that theerror signal fed from the feedback transducer 20 to the drivingamplifier 15 causes the electromechanical motor means 18 of thesound-producing transducer means 10 to be moved in a direction oppositeto the movement causing the error signal in the feedback transducer 20.

FIG. 2 is very similar to FIG. 1 and similar parts will be indicated bythe same reference numerals followed by the letter A. However, in thismodification, an additional feedback amplifier, indicated at 23, isconnected between the feedback transducer 20A and the driving amplifier15A. Otherwise, this modification is substantially the same as the firstform illustrated in FIG. 1 and, therefore, requires no furtherexplanation.

FIG. 3 is a view effectively illustrating one specific embodiment of theform of the invention shown broadly in diagrammatic form in FIG. 1, andcorresponding por tions are indicated by similar reference numerals, followed by the letter B. In this modification, the electromechanicaltranslating motor means 18B of the soundproducing transducer meansindicated generally at 16B comprises an electromagnetic motor whichconsists of a voice coil 24 Wound on a hollow tubular member 25 carriedat the inner end of a conical mechanically vibratable output elementcomprising a loudspeaker cone 26, said electromagnetic motor means alsoincluding a conventional loudspeaker permanent magnet indicated at 27having pole portions positioned so as to cause magnetic flux to passdirectly across the voice coil 24 whereby variations in electric currentfrom the voice coil-driving amplifier 15B will cause longitudinalvibratory movement of the voice coil toward the right and left as viewedin FIG. 3 and thus will effectively vibrate the loudspeaker cone 26 in asimilar manner, since the voice coil 24 is firmly effectively fastenedto the tubular portion 25 carried at the inner end of the loudspeakercone 26. In this connection, it should be noted that the inner end ofthe loudspeaker cone 26 and the tubular portion 25 carried thereby areresiliently centered and mounted for axial piston-like vibratory motionby means of a conventional resilient mounting spider 28 at the inner endof the cone 26 and also by a similar annular corrugated mounting portion29 at the outer edge of the cone 26. Thus, it can be seen thatelectrical current from the voice-coildriving amplifier 1513 willeffectively cause vibration of the loudspeaker cone 26. In thismodification, the feedback transducer is of the capacitive type andincludes the portion shown diagrammatically at 205 and the two effectiveplates of the variable capacitor, which are comprised in effect by anelectrically conductive thin-sheet mem'ber carried by the face of theloudspeaker cone 26, as best seen at 30 in FIG. 5, to which the lead 223is connected as indicated at 31, and the electrically conductive framemeans 32 mounting the entire loudspeaker, to which the lead 21B isconnected as indicated at 33. It should be understood that theelectrically conductive thin-sheet member 34 may comprise a coating ofconductive paint, such as silver paint, or the like, carried by thematerial of which the cone 26 is made and that this comprises thevariable plate or vibratable input element of the capacitive means ofthe capacitive feedback transducer while the electrically conductiveframe 32 comprises the fixed capacitive plate or second element thereof.It should further be noted that the capacitive feedback transducer,indicated in diagrammatic form at 203 in FIG. 3, includes means, whencoupled with the elements 30, 31, 32, and the leads 21B and 22B, tocomprise a complete capacitive transducer. This may be of either theelectrostatic type including polarizing means for applying a polarizedpotential to the frame 32 and the conductive coating 30 andcapacitivedischarge-restricting circuit means in association therewithwhereby to provide an output voltage from the capacitive feedbacktransducer 203 having an amplitude corresponding to the excursion of theconductive coating 30 carried by the cone 26; or the capacitive feedbacktransducer may be of a type such as is indicated more specifically inFIG. 8, including a first frequency modulation step, an intermediateamplification step, and a discrimination step, so as to provide anoutput voltage corresponding to the excursion of the conductive coatingcarried by the loudspeaker cone. This will be described hereinafter inconnection with FIG. 8.

It should be noted that FIG. 3 shows only one soundproducing transducermeans as exemplified by the loudspeaker indicated generally at 108.However, it should be clearly understood that the present invention mayinclude a plurality of such loudspeakers connected in parallel withrespect to a single voice'coil-driving amplifier such as is shown at 153and with respect to a single capacitive feedback transducer (exclusiveof the elements such as the coating 30 and the frame 32) as indicated at20B in FIG. 3. The parallel connection points in the circuitry for thispurpose are indicated respectively at 61 and 62. In this kind ofarrangement, with a plurality of such loudspeakers connected inparallel, all loudspeakers will carry part of the load of correctingerror sounds being generated by all of the other speakers. In such anarrangement, it should be noted that each of the capacitors effectivelyprovided by the conductive coatings 30 and the loudspeaker frames 32 (ofthe type shown in FIG. would be connected together before connectingsame to the single electronic portions of the capacitive feedbacktransducer 20B. Various connection arrangements for such multipleloudspeaker systems may be employed.

FIG. 4 is a schematic diagrammatic view illustrating a slightmodification of the form of the invention illustrated in FIG. 3 andsimilar part will be indicated by the same reference numerals, followedby the letter C. However, in this modification, a feedback amplifier,indicated generally at 34, is connected between the capacitive feedbacktransducer 20C and the amplifier C. Otherwise, this modification issubstantially the same as the form illustrated in FIG. 3 and, therefore,requires no further explanation.

FIG. 6 is a view illustrating one specific form of electrical portionsof the apparatus in a version such as is shown in FIG. 4, showing saidelectrical portions in greater detail, and similar parts will beindicated by the same reference numerals, following by the letter D. Inthis modification, the capacitive feedback transducer indicatedgenerally at D includes the electron tube 35 connected in a cathodefollower circuit and having the lead 22D, which is connected to theconductive coating (not shown in FIG. 6) carried by the loudspeaker cone26, to the grid 36 of the electron tube 35; said lead 22D also beingconnected through a load resistor 37 to a terminal 38 between twocathode resistors 39 and 40 connected between the cathode 41 of electrontube 35 and ground, as indicated at 42. The anode 43 of the electrontube 35 is connected to a terminal 44, which is adapted to be connectedto a suitable source of positive potential, which is adapted to have itsnegative terminal grounded. Said potential source is not shown, sincesuch is well known in the art and does not comprise my real invention.

It will be noted that the cathode follower circuit, just described andassociated with the electron tube 35, provides means for applying apositive polarizing voltage through the lead 22D to the conductivecoating (not shown in detail in FIG. 6, but indicated at 30 in FIG. 5)carried by the loudspeaker cone 26D, it being noted that the frame 32Dof the loudspeaker is at ground potential by reason of connection of thelead 21D to ground as indicated at 45. The circuit components associatedwith the electron tube 35 provide, in effect, acapacitive-discharge-restricting circuit means adapted to prevent rapiddischarge of electrons from the capacitor formed by the conductivecoating carried by the loudspeaker cone 26D, such as is indicated at 30in FIG. 5, and the frame 32D. Therefore, vibratory movement of theloudspeaker cone 26D will be transformed by the polarizing voltageprovided by the cathode follower circuit associated with the electrontube 35, into an error signal potential applied in anelectron-fiow-controlling manner with respect to the control grid 36 andthe cathode 41 of the electron tube 35, whereby current flow through theelectron tube 35 will correspondingly vary and will be coupled throughcapacitor 46 and the cathode resistor 47 to the control grid 48 andcathode 49, respectively, of a second electron tube 50, which comprisesan amplifier, whereby the amplified current flow through said amplifyingelectron tube 50 will be fed through an output circuit to avoice-coildriving amplifier 15D where it joins the normal variableelectrical input signal fed to the voice-coil-driving amplifier 15Dthrough an input terminal 51 of input circuit means indicated generallyat 12D. It should be noted that the lead 17D connected to the voice coil24D corresponds to the lead 17C shown in FIG. 4. However, in thismodification, the other lead 161) is grounded as indicated at 52, sincethe other end of the voice coil 24D is also grounded as indicated at 53.However, it will be noted that the circuit continuity remains the same.

For the purpose of providing a full and complete disclosure,representative values of certain of the components shown in FIG. 6 willbe listed. However, it should be understood that they are not to beconstrued as limiting the invention but are set forth merely toexemplify one working embodiment of the invention. Such representativevalues are as follows:

Resistor 37 may have a value of 150,000 ohms Resistor 39 may have avalue of 3,900 ohms Resistor 40 may have a value of 47,000 ohms Resistor54 may have a value of 220,000 ohms Resistor 47 may have a value of5,000 ohms Resistor 55 may have a value of 100,000 ohms Resistor 56 mayhave a value of 220,000 ohms Resistor 57 may have a value of 390,000ohms Capacitor 46 may have a value of 0.1 microfarad Capacitor 58 mayhave a value of 0.1 microfarad, and Capacitor 59 may have a value of 470micromicrofarads.

Each of the electron tubes 35 and 50 may be l2AX7 tubes.

FIG. 7 is a view similar to FIG. 5 but illustrates a slightly modifiedform of the invention wherein the conductive coating 30E is carried bythe rear surface of the loudspeaker cone 26E. Similar parts areindicated by similar reference numerals followed by the letter B andsince this is the only difference, no further explanation is thoughtnecessary.

FIG. 8 is a view similar to FIG. 4 except that the capacitive feedbacktransducer shown at 20C in FIG. 4 is no longer of the electrostatic typein the modification illustrated in FIG. 8. In the form illustrated inFIG. 8, said capacitive feedback transducer includes a first portionindicated in diagrammatic form at 20F as comprising a frequencymodulated error signal producer, which is connected to the variablecapacitor indicated at connection points 31F and 33E; said transducer20F being of the frequency modulation type adapted to be connected to atuned circuit associated with an oscillation generator for effectivelyvarying the frequency of output oscillations therefrom which are thenfed to an amplifier such as is indicated diagrammatically at MP in FIG.8, and which are then fed to a frequency discriminator, such as isindicated diagrammatically at 61) in FIG. 8, and which is adapted toconvert the amplified frequency modulated error signal into acorresponding variable potential error signal which is fed into thevoice-coil-amplifier F in the same manner as described hereinbefore. Inother words, in the modification of the invention illustrated in FIG. 8,the only difference is that a frequency modulation and discriminationtype of capacitive transducer is substituted for the electrostatic typeof capacitive transducer shown in FIG. 6 in detail.

It should be noted that the apparatus of the present invention isreadily adapted for use with more complex speaker systems, includingwhat are known in the art as tweeters, woofers, crossover networks, andthe like.

It should be understood that the figures and the specific descriptionthereof set forth in this application are for the purpose ofillustrating the present invention and are not to be construed aslimiting the present invention to the precise and detailed specificstructure shown in the figures and specifically described hereinbefore.Rather, the real invention is intended to include substantiallyequivalent constructions embodying the basic teachings and inventiveconcept of the present invention.

I claim:

1. Self-correcting high fidelity sound reproducing apparatus,comprising: electroacoustic sound-producing transducer means including amechanically vibratable output element effectively coupleable to ambientatmosphere, including electrical input circuit means, and includingelectromechanical translating motor means effectively electricallyenergizably coupled to said electrical input circuit means andeffectively drivingly coupled to said mechanically vibratable outputelement for vibrating same in a manner corresponding to a variableelectric input signal fed into said electrical input circuit means; andcapacitive mechano-electrical feedback transducer means including avibratable input element and a second element in capacitive relationshipto each other, said vibratable input element of said capacitivemechano-electrical feedback transducer means comprising an electricallyconductive thinsheet member co-extensive with substantially the entiresurface area of at least one side of said vibratable output element ofsaid sound-producing transducer means and physically carried by saidvibratable output element in integrating and summing relationship withrespect to said vibratable output element whereby to effectivelyintegrate and sum vibratory variations in different portions of saidvibratable output element, and said feedback transducer means beingeffectively electrically coupled, in negative feedback relationship,with respect to said electrical input circuit means.

2. Self-correcting high fidelity sound reproducing apparatus,comprising: electroacoustic sound-producing transducer means including amechanically vibratable output element consisting of a conical memberhaving its interior conical surface coupled to ambient atmosphere,including electrical input circuit means, and including electromagneticmotor means effectively electrically energizably coupled to saidelectrical input circuit means and effectively drivingly coupled to saidconical mechanically vibratable output element for vibrating same in amanner corresponding to a variable electric input signal fed into saidelectrical input circuit means; and capacitive mechanoelectricalfeedback transducer means including a vibratable input element and asecond element in capacitive relationship to each other, said vibratableinput element of said capacitive mechano-electrical feedback transducermeans comprising a conical electrically conductive thinsheet membercoextensive with substantially the entire conical surface area of atleast one side of said conical vibratable output element of saidsound-producing transducer means and physically carried by said conicalvibratable output element in integrating and summing relationship withrespect to said conical vibratable output element whereby to effectivelyintegrate and sum vibratory variations in different portions of saidconical vibratable output element, and said two elements of saidfeedback transducer means being effectively electrically coupled, innegative feedback relationship, with respect to said electrical inputcircuit means.

3. Self-correcting high fidelity sound reproducing apparatus,comprising: electromagnetic sound-producing transducer means including amechanically vibratable output element consisting of a conical memberhaving its interior conical surface coupled to ambient atmosphere,including electrical input circuit means, and including electromagneticmotor means provided with a voice coil and also including a magnetproviding a magnetic field encompassing said voice coil, said voice coilbeing effectively electrically energizably coupled to said electricalinput circuit means and effectively drivingly coupled to said conicalmechanically vibratable output element for vibrating same in a mannercorresponding to a variable electric input signal fed into saidelectrical input circuit means; and capacitive mechano-electricalfeed-back transducer means including a vibratable input element and asecond element in capacitive relationship to each other, said vibratableinput element of said capacitive mechano-electrical feedback transducermeans comprising a conical electrically conductive thin-sheet membercoextensive with substantially the entire conical surface area of atleast one side of said conical vibratable output element of saidsound-producing transducer means and physically carried by said conicalvibratable output element in integrating and summing relationship withrespect to said conical vibratable output element whereby to effectivelyintegrate and sum vibratory variations in different portions of saidconical vibratable output element, and said two elements of saidfeedback transducer means being effectively electrically coupled, innegative feedback relationship, with respect to said electrical inputcircuit means.

4. Self-correcting high fidelity sound reproducing apparatus,comprising: electromagnetic sound-producing transducer means including amechanically vibratable output element consisting of a conical memberhaving its interior conical surface coupled to ambient atmosphere,including electrical input circuit means, and including electromagneticmotor means provided with a voice coil and also including a magnetproviding a magnetic field encompassing said voice coil, said voice coilbeing effectively electrically energizably coupled to said electricalinput circuit means and effectively drivingly coupled to said conicalmechanically vibratable output element for vibrating same in a mannercorresponding to a variable electric input signal fed into saidelectrical input circuit means; said electrical input circuit meansincluding amplifier means; and capacitive mechano-electrical feedbacktransducer means including a vibratable input element and a secondelement in capacitive relationship to each other, said Vibratable inputelement of said capacitive mechano-electrical feedback transducer meanscomprising a conical electrically conductive thin-sheet membercoextensive with substantially the entire conical surface area of atleast one side of said conical vibratable output element of saidsound-producing transducer means and physically carried by said conicalvibratable output element in integrating and summing relationship withrespect to said conical vibratable output element whereby to effectivelyintegrate and sum vibratory variations in different portions of saidconical vibratable output element, and said two elements of saidfeedback transducer means being effectively electrically coupled, innegative feedback relationship, with respect to said amplifier means ofsaid electrical input circuit means.

5. Self-correcting high fidelity sound reproducing apparatus,comprising: electromagnetic sound-producing transducer means including amechanically vibratable output element consisting of a conical memberhaving its interior conical surface coupled to ambient atmosphere,including electrical input circuit means, and including electromagneticmotor means provided with a voice coil and also including a magnetproviding a magnetic field encompassing said voice coil, said voicebeing eifectively electrically energizably coupled to said electricalinput circuit means and effectively drivingly coupled to said conicalmechanically vibratable output element for vibrating same in a mannercorresponding to a variable electric input signal fed into saidelectrical input circuit means; said electrical input circuit meansincluding amplifier means provided with a control electrode; andcapacitive mechanoelectrical feedback transducer means including avibratable input element and a second element in capacitive relationshipto each other, said vibratable input element of said capacitivemechano-electrical feedback transducer means comprising a conicalelectrically conductive thinsheet member coextensive with substantiallythe entire conical surface area of at least one side of said conicalvibratable output element of said sound-producing transducer means andphysically carried by said conical vibratable output element inintegrating and summing relationship with respect to said conicalvibratable output element 'whereby to effectively integrate and sumvibratory variations in different portions of said conical vibratableoutput element, and said two elements of said feedback transducer meansbeing effectively electrically coupled, in negative feedbackrelationship, with respect to said control electrode of said amplifiermeans of said electrical input circuit means.

6. Self-correcting high fidelity sound reproducing apparatus,comprising: electromagnetic sound-producing transducer means including amechanically vibratable output element consisting of a conical memberhaving its interior conical surface coupled to ambient atmosphere,including electrical input circuit means, and including electromagneticmotor means provided with a voice coil and also including a magnetproviding a magnetic field encompassing said voice coil, said voice coilbeing effectively electrically energizably coupled to said electricalinput circuit means and eifectively drivingly coupled to said conicalmechanically vibratable output element for vibrating same in a mannercorresponding to a variable electric input signal fed into saidelectrical input circuit means; said electrical input circuit meansincluding amplifier means provided with a control electrode; andcapacitive mechano-electrical feedback transducer means including avibratable input element and a second element in capacitive relationshipto each other, said vibratable input element of said capacitivemechano-electrical feedback transducer means comprising a conicalelectrically conductive thin-sheet member coextensive with substantiallythe entire conical surface area of at least one side of said conicalvibratable output element of said sound-producing transducer means andphysically carried by said conical vibratable output element inintegrating and summing relationship with respect to said conicalvibratable output element whereby to eifectively integrate and sumvibratory variations in different portions of said conical vibratableoutput element, and said two elements of said feedback transducer meansbeing effectively electrically coupled, in negative feedbackrelationship, with respect to said control electrode of said amplifiermeans of said electrical input circuit means, said second element ofsaid feedback transducer means comprising an electrically conductiveframe means vibratably mounting said conical mechanically vibratableoutput element of said sound-producing transducer means.

References Cited in the file of this patent UNITED STATES PATENTS

